Geologic formations below the surface of the earth may contain reservoirs of oil and gas, which are retrieved by drilling one or more boreholes into the subsurface of the earth. The boreholes are also used to measure various properties of the boreholes and the surrounding subsurface formations.
Oil and gas retrieval and measurement processes often involve the use of multiple boreholes. Multiple boreholes are useful, for example, in maximizing oil and gas retrieval from a formation and establishing sensor arrays for formation evaluation (FE) purposes.
An example of a multiple borehole oil and gas retrieval system is a Steam Assisted Gravity Drainage (SAGD) system that is used for recovering heavy crude oil and/or bitumen from geologic formations, and generally includes heating the bitumen through an injection borehole until it has a viscosity low enough to allow it to flow into a parallel recovery borehole. As used herein, “bitumen” refers to any combination of petroleum and matter in the formation and/or any mixture or form of petroleum, specifically petroleum naturally occurring in a formation that is sufficiently viscous as to require some form of heating or diluting to permit removal from the formation.
Generally, implementation of a multiple borehole system includes detecting a location of a first borehole when drilling a second borehole in order to avoid contact between the boreholes and/or accurately position the boreholes relative to one another. Such detection may involve the use of antennas that act as transmitters and receivers to interrogate an earth formation. Examples of such antennas include so-called “slot” design antennas, such as “Z-type” antennas (“Z-antennas”) typically used in multi-frequency and multi-spacing propagation resistivity (“MPR”) tools and “X-type” antennas (“X-antennas”) typically used in azimuth propagation resistivity (“APR”) tools. Accurate detection of borehole position can be difficult, as direct coupling of measurement signals between measurement transmitters and receivers can overshadow measurement signals.